(특이하거나 분명한 해답이 없어서) 흥미로운 CO의 정전기 퍼텐셜

(특이하거나 분명한 해답이 없어서) 흥미로운 CO의 정전기 퍼텐셜

Intriguing Electrostatic Potential of CO: Negative Bond-ends and Positive Bond-cylindrical-surface

 

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[저자]

Hahn Kim(1), Van Dung Doan(2), Woo Jong Cho(2), Rosendo Valero(2), Zahra Aliakbar Tehrani(2), Jenica Marie L. Madridejos(2) & Kwang S. Kim(2)

 

(1) Department of Chemistry, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea.

(2) Department of Chemistry, School of Natural Science, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689-798, Korea. Correspondence and requests for materials should be addressed to K.S.K. (email: kimks@unist.ac.kr)

 

2015년 11월 6일 출판

 

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[초록]

The strong electronegativity of O dictates that the ground state of singlet CO has positively charged C and negatively charged O, in agreement with ab initio charge analysis, but in disagreement with the dipole direction.

( O의 강한 전기음성도는 바닥상태에 있는 singlet CO는 양전하를 띤 C와 음전하를 띤 O를 갖고 있다는 것을 지시하는데, 이것은 ab initio 전하 분석과는 일치하고, 쌍극자 방향과는 일치하지 않는다. )

Though this unusual phenomenon has been fairly studied, the study of electrostatic potential (EP) for noncovalent interactions of CO is essential for better understanding.

Here we illustrate that both C and O atom-ends show negative EP (where the C end gives more negative EP), favoring positively charged species, whereas the cylindrical surface of the CO bond shows positive EP, favoring negatively charged ones. This is demonstrated from the interactions of CO with Na+, Cl–, H2O, CO and benzene. It can be explained by the quadrupole driven electrostatic nature of CO (like N2) with very weak dipole moment. The EP is properly described by the tripole model taking into account the electrostatic multipole moments, which has a large negative charge at a certain distance protruded from C, a large positive charge on C, and a small negative charge on O.

We also discuss the EP of the first excited triplet CO.

 

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[토의]

In summary, we note that both C and O atom-ends of the CO bond show negative EP (where the C end is slightly more negative), whereas the cylindrical surface of the CO bond axis shows positive EP.

This has been properly described by the tripole model which shows the three regions comprised of two negative EP regions around C and O atom-ends and one positive region around the cylindrical surface of the CO bond between C and O. Thus, both C and O atom-ends favor positively charged sites, while the cylindrical surface (in particular near the C atom) favors negatively charged sites. Such phenomena are demonstrated based on the interactions of CO with a cation/anion, H2O, and benzene. Clearly CO should not be considered as a molecule with a simple weak dipole moment, but needs to be interpreted as a quadrupole driven molecule (like N2) with very weak dipole moment. On the other hand, the triplet COt has a significant dipole moment; accordingly, the O-end shows negative EP, while the C-end shows positive EP. The present results could further facilitate diverse gas phase experiments involving CO-bound complexes.

 

 

 

요약하면,
1) CO 결합의 양쪽 말단의 C 원자와 O 원자 둘 다 음전하를 나타낸다.
단, C쪽이 약간 더 음전하.
2) CO 결합 축의 원통 표면은, 즉 CO의 결합 전자들이 밀집되어 있는 공간은 양전하를 나타낸다.
단, C쪽이 약간 더 양전하.

 

 

[ 자료출처: www.nature.com ]

 

 

[ 관련 글1 https://ywpop.tistory.com/2632 ]
[ 관련 글2 https://ywpop.tistory.com/5228 ]

 

 

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고등학교 과정에서는
극성 무극성 분자를 다룰 때,
CO는 제외하는 것이 좋을 것 같다.
( 또는 완전 조심히 다루어야 할 것 같다. )
 

음전하가 O에 있다는 것을, 아니면 C에 있다는 것을
딱 잘라 설명하기 곤란할 것이기 때문이다.
 

CO의 정전기적 특성이 얼마나 독특했으면,
달랑 2개의 가벼운 원자로 이루어진
이 간단한 분자의 극성이
2015년까지, 그것도 네이처에 실릴 정도로,
연구대상이 되었을까?